1. Field of the Invention
This invention relates to graft polymerization of synthetic rubber and methyl methacrylate polymers and copolymers.
2. Description of the Prior Art
In the rubber modified impact polystyrene art, it is well known to use alkyl methacrylate as comonomers with styrene, which are polymerized in the presence of synthetic rubbers such as butadiene-styrene copolymers. Roche et al, U.S. Pat. No. 2,941,977, disclose a homogeneous and inseparable dispersion of the copolymer ingredients with one another. Lee U.S. Pat. No. 3,267,178 discloses graft polymers prepared by dissolving or dispersing rubbery butadiene polymer in monomers, heating first in mass while agitating to partially polymerize the monomers, then suspending the partially polymerized liquid in an inert aqueous medium at elevated temperatures to polymerize the remaining monomers.
Lunk et al, U.S. Pat. No. 3,178,489, disclose a bulk or mass polymerization of styrene-methyl methacrylate copolymer in certain ratios in the presence of dissolved styrene/butadiene copolymer in two or three successive stages. British Pat. No. 1,489,263 shows polymerization of styrene by mass polymerization in the presence of dissolved synthetic rubber in three successive zones in a devolatilizing extruder to produce high impact polystyrene. Kelsey, U.S. Pat. No. 4,080,406 shows polymerization of vinyl aromatic monomer and methyl or ethyl methacrylate in the presence of a synthetic rubber by different processes, one of which is a continuous or partially continuous process wherein solution is continuously introduced and removed from a stirred reactor at a constant 30-50% solids content; then completion of the polymerization at higher temperatures for several hours in a second stage. Shimada et al, U.S. Pat. No. 3,900,453 teach polymerization of methacrylates continuously in a stirred reactor at temperatures above 130.degree. C. and below 160.degree. C. The monomer feed contains mercaptan as well as free radical initiator. Among the modifier materials are polymers such as polystyrene and synthetic rubbers "incorporated in the polymerization or volatile removing steps, or after the volatile removing step. In most cases," Shimada et al say, "it is preferred to incorporate these additives after the polymerization step".
None of the prior art processes in this field produce products which have excellent clarity, impact strength, rigidity, and melt flow properties.